Neuroscientists are interested in how brains interact socially. One of the main topics of study is ‘mentalizing’ aka ‘theory of mind’, the ability to accurately attribute mental states – such as beliefs and emotions – to other people.

It is widely believed that the brain has specific areas for this – i.e. social “modules” (although today most neuroscientists are shy about using that word, it’s basically what’s at issue.)

But two new papers out this week suggest that people can still mentalize successfully after damage to “key parts of the theory of mind network”.

Herbet et al, writing in Cortex, showed few effects of surgical removal of the right frontal lobe in 10 brain tumour patients. On two different mentalizing tasks, they showed that removal caused either no decline in performance, or only a transient one.

They describe a patient suffering from frontotemporal dementia (FTD), whose left temporal lobe was severely atrophied. He’d lost the use of language, but he did quite normally on theory of mind tests adapted to be non-linguistic.

In both papers, these patients don’t have those parts of the brain that are most activated in fMRI studies of mentalizing. Where the blobs on the brain normally go, they have no brain.

Here’s an example from Michel et al showing the average peak activation spots seen in mentalizing tasks, projected onto the brain of the FTD patient and a control:

As you can see, however, the right side of the brain was in much better shape. So I think that’s a major caveat here. All of these patients lost large parts of one half of the brain, but none (as far as I can tell) lacked the corresponding areas from both sides.

So it could be that the inferior frontal cortex and the temporal pole are indeed key to theory of mind, but you can get away with only one of each. The fact that we have a pair of each, one left one right, provides redundancy. A bit like kidneys.

This is quite plausible, but it’s still interesting that the brain seems to be able to almost seamlessly cope with the loss of one of the halves.

And it does make you question what it means when activity in one of these areas is found to be reduced in (say) people with autism – on one side of the brain only. If activity can be zero on one side, without any problems, does it matter if it’s down a little?

Good point, thanks. A priori, I find it hard to see why ToM would be lateralized, so my default assumption is that it’s not. Then again a priori there’s no reason language would be lateralized but it is.

M Peirce

For what it’s worth there are plenty of a priori reasons for expecting language to be lateralized, provided that we subscribe to current views that left hemisphere functions tend to be “analytic” while the right tend to be “holistic.”

A key feature of language is that it is “modular.” Roughly, this means that you can replace a term in a sentence, and (a) still have a meaningful sentence, while also (b) the meanings of the other terms in that sentence are left unchanged. This contrasts with holism, where changes in any given part of a whole typically involves changing many other parts of that same whole.

Anna O

Evidence from lesion data actually points to a critical role played by the left TPJ in theory of mind (Samson et al., 2004). It is also worth noting that there is a large body of evidence which indicates that the TPJ is involved in several other aspects of perception, cognition and behavior. This is often simply overlooked by the mental state reasoning community when ascribing functions to this brain structure.

The problem with left TPJ lesions is that they often result in some degree of aphasia, as was observed in two of the three patients in that study. However, these authors (one of whom has commented above) did another study that reduced language demands:

John Simons also raises an excellent point about discrepancies between methodologies.

usethebrainsgodgiveyou

“And it does make you question what it means when activity in one of
these areas is found to be reduced in (say) people with autism – on one
side of the brain only. If activity can be zero on one side, without any
problems, does it matter if it’s down a little?”

What about not down, but inversed? Divergent thinking…Say, down in L language areas, but up in R language areas

…just a mom.

Jon Simons

There was a fascinating paper published a few years ago by Chris Bird and colleagues from UCL (including Uta Frith) reporting a case with extensive medial frontal damage (including the areas typically linked with theory of mind), who was impaired on some executive tasks but nevertheless had pretty much normal performance on theory of mind tasks.

There are in fact quite a number of similar papers in different areas of cognitive neuroscience showing discrepancies between fMRI and lesion evidence. In fact, one might go as far as to say that consistent results between the methods are not as common as often imagined. Which of course raises a number of interesting questions about what these methods are measuring and whether we should expect consistency between them.

Ian Apperly

Important findings. Tricky for a “one module/one miracle”
view of the neural basis of mentalizing. But much evidence already suggests that multiple processes contribute to mentalizing (personal interest declared), and their importance varies across tasks. For example, Herbert et al.’s tasks clearly involve mentalizing, but unlike many mentalizing tasks they do not create major conflict between the perspective of the target and that of the participant. Numerous studies suggest that managing such conflict may be a key function of ventro-lateral prefrontal cortex during mentalizing, making it less surprising that patients with damage to this region succeed on tasks that do not make this critical functional demand. Neuroskeptic’s point about possible redundancy in the neural regions supporting mentalizing is important, but not necessary to explain these findings because mentalizing involves multiple processes and mentalizing tasks are not all created equal.

Absent is not the same as damaged or dysfunctional. The 2 halves of the cortex function quite well if the corpus callosum is cut. But please remember Phineas Gage. The consequence of damage to the frontal lobes may depend on the degree of socialization of the midbrain and pons. There is so much that we don’t know.

Marc

Very interesting stuff. Really makes you realize just how amazing the brain is and imagine what other capabilities it has in store for us in future research on the subject.if the hemispheres are indeed working independently maybe there is a possibility in the future for transplanting separate “modules” from one person to another.

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Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.